Modeling Barcelona sidewalks: A high resolution urban scale assessment of the geometric attributes of the walkable network

Within the framework of urban pedestrian networks, this paper presents a method of modeling the street network from the perspective of foot traffic, beyond the vehicle-focused street centerline representation approach in transportation research. A scalable method to extract the centerlines of the complete walkable urban area from its polygon representation at a one-meter resolution is discussed, using open-source tools. To evaluate the betweenness centrality in a spatially directed graph, the process is applied to the study of the ‘walkable Barcelona’, focusing on three key parameters: 1) the street width, 2) the longitudinal slope, and 3) the crosswalks connecting the sidewalk platforms. The results identify the uneven distribution of these parameters within a complex urban fabric, and the high-resolution cartography allows the identification of critical areas within the network, introducing future lines of research and applications of the workflow. This is especially relevant considering the increasing awareness of citizens and the urban agendas worldwide, aimed at improving and widening the sidewalk infrastructure that supports local activity in cities.

The authors would like to thank the Academic editors and the Reviewers for the opportunity to address the comments. The authors hope that the Editors and Reviewers will be satisfied with the amendments which we have made to the manuscript after considering the feedback provided.
In relation to the main points indicated at the beginning of the response received, we have corrected or improved the following aspects:

1) Text is too long. If possible try to shorten it without losing quality
The manuscript text has been made substantially more concise without compromising the explanation of the workflow. The reduction in length has been achieved reducing unnecessary detail in some of the explanations; some of these details are now summarized graphically in a new figure and another that has been updated, and some paragraphs have been removed as it has been considered that excessive implementation details made the readability of the text more difficult. The authors believe that the text is in its current form much easier to follow without losing quality.

2) In the webpages access date needs to be added
The webpages access dates have been included in the text. We apologize for this oversight.
3) There are very few scholarly articles cited in the text, and very many websites and Spanishlanguage items. Please add some/any foreign publications From our perspective, the paper is based on an introductory discussion on the existing bibliography on the issue and the application of some libraries published in open repositories and websites. The development of the methodology described in the paper does not require of further citation along the central chapters of the paper. However, we have been completed the text with some publications. The paper now has around 64 cited bibliography, 19 of them are Spanish research focusing on the case-study discussion.

4) Some typos in the text, e.g. line 595 and other
The text has been thoroughly revised and any typos in the manuscript have been corrected. The authors thank the reviewers for pointing this out.

5) Some figures are unreadable e.g. 12 and 17
The figures have been included again in full resolution and new typographies. Also, we believe the lack of quality might be a consequence of the compression in the content management system. The authors apologize if they are difficult to read. Please note that the figures might have changed numbering as a new figure has been introduced.
6) It would be nice to see a table showing the data reduction during the workflow in terms of quantities (e.g. numbers for input data polygons/lines, node count, segments (etc.) before/after aggregation at certain steps in the process, and processing time needed) A new figure has been included in the manuscript that summarizes the changes in geometric complexity in each of the processing steps, and the details regarding the processing time of the workflow. This figure has contributed to significantly reduce the length of the manuscript and consolidate in a single place many details scattered in the text. The authors appreciate the suggestion of the reviewer for pointing this possibility.
7) It would also be nice to see the actual code that was used to produce graphics The authors are working on releasing the code in the future with proper documentation and streamline the workflow for external usage. However, the code can be inspected on request.

8) A comparison with other data sources or on-site observations (examples/ground truth) could help to better critically reflect the workflow results and illustrate where the model/workflow resulted in errors, ambiguities, or inaccuracies, either due to data or method used
The authors agree with the reviewers that a comparison with the ground truth would be interesting to be included, but they considered that it would increase the length of the manuscript excessively. It is however discussed in subsection 2.1. Figures 1, 3 , 4, 5, 6, 7, 8, 9, 11, 12, 13, 15 and 17 (CC BY 4.0), which means that the manuscript, images, and Supporting Information files will be freely available online, and any third party is permitted to access, download, copy, distribute, and use these materials in any way, even commercially, with proper attribution. For these reasons, we cannot publish previously copyrighted maps or satellite images created using proprietary data, such as Google software (Google Maps, Street View, and Earth). For more information, see our copyright guidelines: http://journals.plos.org/plosone/s/licenses-and-copyright.

9) We note that
The figures are not using satellite images but base Cartography from CartoBCN open data repository (Barcelona City Council), under CC BY 4.0. This information has been added to each caption.

Reviewers' comments:
Reviewer #1: I would like to congratulate the author to revised and improve the quality of the manuscript. The manuscript is now written very well and the analysis carried out in this research is new and the results represents the actual study performed.
The authors appreciate the reviewer feedback. The manuscript has been revised to address the issues pointed out by the reviewers.
Reviewer #2: (…) The following detailed comments are intended to correct some of the shortcomings of the article. Detailed comments Text is written in a logical and thoughtful way, creating a coherent whole, in accordance with the writing regime of scientific paper (IMRaD). The method of presentation, comprehensive introduction and very interesting and thoughtful practical examples deserve praise. Below a comments for corrections: 1) In my opinion text is too long in some way it might be shorten which will affect on its better reception.
The manuscript text has been made substantially more concise without compromising the explanation of the workflow. The reduction in length has been achieved reducing unnecessary detail in some of the explanations; some of these details are now summarized graphically in a new figure and another that has been updated, and some paragraphs have been removed as it has been considered that excessive implementation details made the readability of the text more difficult. The authors believe that the text is in its current form much easier to follow without losing quality.

2) In the webpages access date needs to be added
This information has been added to the text. The authors thank the reviewer for pointing this out.

3) There are very few scholarly articles cited in the text, and very many websites and Spanishlanguage items. Please add some/any foreign publications
From our perspective, the paper is based on an introductory discussion on the existing bibliography on the issue and the application of some libraries published in open repositories and websites. The development of the methodology described in the paper does not requires of further citation along the central chapters of the paper. However, we have been completed the text with some publications. The paper now has around 64 cited bibliography, 19 of them are Spanish research focusing on the case-study discussion.

4) See remark 2, regarding references
This information has been added to the text. We do thank very much the reviewer for these key references that might be related to the topic of the paper. The methodology is applied to sidewalks as polygon geometries with specific attributes. However, further research might be helpful to find other utilities in other fields of knowledge such as geography. Unfortunately, in order to make the paper more concise, we consider that this discussion should be addressed in future research.

6) Some typos in the text, e.g. line 595 and other
The text has been fully reviewed. We apologize for this oversight.

7) Some figures and unreadable e.g. 12 and 17
The figures have been included again in full resolution and new typographies. Also, we believe the lack of quality might be a consequence of the compression in the content management system. The authors apologize if they are difficult to read. Please note that the figures might have changed numbering as a new figure has been introduced.
Reviewer #3: General Statement: The paper demonstrates a detailed implementation workflow for processing urban spatial information to extract sidewalks in Barcelona as a case study. These are used to generate pedestrian network information such as shortest paths, network costs for different edges and segments or summary metrics for different distributions. The results are generally interpret, listing benefits of the implementation and several opportunities for application.
1. The strengths of the paper are its nice graphics and the holistic and good explanations for taking different routes and combining different tools and software along the way, including the descriptions of dead ends. I am no expert in network or topology processing, so I cannot comment on the overall significance or novelty of this papers contributions, particularly for the sub-field of pedestrian network extraction. The short literature review suggests that there is limited comparable work available. That said, the results and process look quite polished, the discussion is reflected and comprehensive, and I would argue that the biggest value for readers lies in the practical implementation and the decision tree that is described in the text. The text is easy to follow and overall well written.
The authors appreciate the reviewer feedback. The manuscript has been revised to address the issues pointed out by the reviewers.
2. Unfortunately, the decision tree for the workflow is not shown as a figure and the practical implementation can only be followed using the text. Figure 2 is a good first overview of the overall workflow, but it is linear, whereas in the manuscript, positively, several dead ends are described, software or data limits, alternative ways or sensitivity checks being done that are not visible in Fig 2. To someone who wants to transfer the workflow to another city, a decision tree would be quite helpful, indicating these options and alternative routes for adaption (e.g. in case of data availability and other changing parameters).
These details are now summarized graphically in a new figure (Fig. 3) with the workflow steps to produce a directed graph from the source data. The complexity of the data is expressed as node and vertex count at each step, in a logarithmic scale. The processing time required is shown as elapsed minutes from the initial condition.